1. Field of the Invention
This invention generally relates to an apparatus for reproducing information from a recording medium such as an optical disc. This invention specifically relates to an information reproducing apparatus including a waveform equalization circuit for processing a reproduced signal of a run-length-limited code.
2. Description of the Related Art
Japanese patent application publication number 10-106161 discloses an optical information reproducing apparatus based on a PRML (partial response maximum likelihood) system. In the apparatus of Japanese patent application 10-106161, information of a run-length-limited code is reproduced from an optical disc through a reproducing section, and a transversal filter subjects the reproduced waveform to partial-response equalization. The output signal of the transversal filter is decoded into binary data by a maximum-likelihood decoder. The apparatus of Japanese patent application 10-106161 includes a parameter setting device which selects intersymbol-interference imparting values in the partial-response equalization in accordance with the characteristics of the reproduced waveform. Also, the parameter setting device sets tap coefficients of the transversal filter and a decision point signal level for the maximum-likelihood decoder as parameters in response to the selected intersymbol-interference imparting values.
The apparatus of Japanese patent application 10-106161 premises that the optical disc has predetermined pits (reference pits) representative of parameter-setting reference data. Accordingly, the apparatus of Japanese patent application 10-106161 fails to implement suitable waveform equalization for an optical disc which lacks such predetermined pits.
Japanese patent application publication number 7-192270 discloses an apparatus for reproducing a digital signal of a run-length-limited code from an optical disc. The apparatus of Japanese patent application 7-192270 uses a method suited for a high information recording density. The method in Japanese patent application 7-192270 performs ternary equalization whose objects are only an amplitude except for points corresponding to a data train provided with a minimum code inverting gap among points just before or just after the inverting position of a code and an amplitude at the inverting position of the code.
In the apparatus of Japanese patent application 7-192270, a signal is read from an optical disc by an optical head, and the read signal is applied through an amplifier to an equalizer. A decider following the equalizer discriminates the level of the output signal of the equalizer. The decider includes two comparators. The output signals of the comparators are fed to an error calculation circuit as level discrimination results. Since the decider includes the two comparators, the signal processing by the decider is relatively complicated and the level discrimination results provided by the decider tend to be adversely affected by noise and signal distortion.
It is an object of this invention to provide an improved reproducing apparatus.
A first aspect of this invention provides a reproducing apparatus comprising first means for reproducing a signal of a run-length-limited code from a recording medium; a transversal filter subjecting the signal reproduced by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; second means for detecting whether or not the signal reproduced by the first means corresponds to a peak point, and generating peak-point information in response to a result of said detecting; a delay circuit responsive to the peak-point information generated by the second means for outputting at least three successive samples of the peak-point information; a temporary decision device for calculating a temporary decision value of the equalization-resultant signal on the basis of a PR mode signal, an RLL mode signal, the successive samples of the peak-point information which are outputted from the delay circuit, and an actual value of the equalization-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; third means for calculating a difference between the temporary decision value of the equalization-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; and fourth means for controlling the tap coefficients of the transversal filter in response to the error signal generated by the third means so as to minimize the error signal.
A second aspect of this invention is based on the first aspect thereof, and provides a reproducing apparatus wherein at least one of the PR mode signal and the RLL mode signal remains fixed.
A third aspect of this invention is based on the first aspect thereof, and provides a reproducing apparatus wherein the second means comprises an A/D converter for converting the signal reproduced by the first means into a digital signal, means for subjecting the digital signal generated by the A/D converter to a re-sampling process to generate a re-sampling resultant signal, means for feeding the re-sampling resultant signal to the transversal filter, and means for detecting whether or not the digital signal generated by the A/D converter corresponds to a peak point, and generating peak-point information in response to a result of said detecting.
A fourth aspect of this invention provides a reproducing apparatus comprising first means for reproducing a signal of a run-length-limited code from a recording medium; a transversal filter subjecting the signal reproduced by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; second means for detecting whether or not the equalization-resultant signal generated by the transversal filter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; a delay circuit responsive to the peak-point information generated by the second means for outputting at least three successive samples of the peak-point information; a temporary decision device for calculating a temporary decision value of the equalization-resultant signal on the basis of a PR mode signal, an RLL mode signal, the successive samples of the peak-point information which are outputted from the delay circuit, and an actual value of the equalization-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; third means for calculating a difference between the temporary decision value of the equalization-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; and fourth means for controlling the tap coefficients of the transversal filter in response to the error signal generated by the third means so as to minimize the error signal.
A fifth aspect of this invention is based on the fourth aspect thereof, and provides a reproducing apparatus wherein the second means comprises a peak detector for detecting a point at which a level represented by the equalization-resultant signal peaks, and generating the peak-point information in response to said detected point.
A sixth aspect of this invention is based on the fourth aspect thereof, and provides a reproducing apparatus wherein the second means comprises means for comparing a phase of a bit clock signal and a phase of a point at which a level represented by the equalization-resultant signal peaks, and generating a phase error signal in response to said phase comparing.
A seventh aspect of this invention is based on the first aspect thereof, and provides a reproducing apparatus wherein the type of the partial-response waveform equalization which is represented by the PR mode signal is expressed as PR (a, b, xe2x88x92b, xe2x88x92a), and the successive samples of the peak-point information are three successive samples, and wherein the temporary decision device comprises means for calculating a value P on the basis of the successive samples of the peak-point information, the value P being equal to axc2x7G when at least one of the successive samples of the peak-point information except a central sample corresponds to a peak point, the value P being equal to (a+b)xc2x7G when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for detecting a polarity of a level represented by the equalization-resultant signal which occurs when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for calculating the temporary decision value on the basis of the calculated value P and the detected polarity, and means for setting the temporary decision value to xe2x80x9c0xe2x80x9d when none of the successive samples of the peak-point information corresponds to a peak point, where G denotes a gain factor.
An eighth aspect of this invention is based on the first aspect thereof, and provides a reproducing apparatus wherein the type of the partial-response waveform equalization which is represented by the PR mode signal is expressed as PR (a, b, xe2x88x92b, xe2x88x92a), and the successive samples of the peak-point information are five successive samples, and wherein the temporary decision device comprises means for calculating a value P on the basis of the successive samples of the peak-point information, the value P being equal to axc2x7G when at least one of second and fourth samples among the successive samples of the peak-point information corresponds to a peak point, the value P being equal to (a+b)xc2x7G when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for detecting a polarity of a level represented by the equalization-resultant signal which occurs when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for calculating the temporary decision value on the basis of the calculated value P and the detected polarity, and means for setting the temporary decision value to xe2x80x9c0xe2x80x9d when none of second, third, and fourth samples among the successive samples of the peak-point information corresponds to a peak point, where G denotes a gain factor.
A ninth aspect of this invention is based on the first aspect thereof, and provides a reproducing apparatus wherein the first means comprises means for reproducing the signal of the run-length-limited code from the recording medium in a tangential push-pull method.
A tenth aspect of this invention provides a reproducing apparatus comprising first means for reproducing a signal of a run-length-limited code from a recording medium; a transversal filter subjecting the signal reproduced by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; a temporary decision device for calculating a temporary decision value of the equalization-resultant signal according to a temporary decision algorithm; second means for calculating a difference between the temporary decision value of the equalization-resultant signal and an actual value thereof, and generating an error signal in response to the calculated difference; third means for controlling the tap coefficients of the transversal filter in response to the error signal generated by the second means so as to minimize the error signal; and fourth means for changing the temporary decision algorithm used by the temporary decision device between a first predetermined algorithm corresponding to PR (a, b, b, a) waveform equalization and a second predetermined algorithm corresponding to PR (a, b, xe2x88x92b, xe2x88x92a) waveform equalization.
An eleventh aspect of this invention provides a reproducing apparatus comprising first means for reproducing a signal of a run-length-limited code from a recording medium; a transversal filter subjecting the signal reproduced by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; second means for detecting whether or not the signal reproduced by the first means corresponds to a zero-cross point, and generating 0-point information in response to a result of said detecting; third means for detecting whether or not the signal reproduced by the first means corresponds to a peak point, and generating peak-point information in response to a result of said detecting; fourth means for selecting one of the 0-point information generated by the second means and the peak-point information generated by the third means; a delay circuit responsive to the point information selected by the fourth means for outputting at least three successive samples of the selected point information; a temporary decision device for calculating a temporary decision value of the equalization-resultant signal on the basis of a PR mode signal, an RLL mode signal, the successive samples of the selected point information which are outputted from the delay circuit, and an actual value of the equalization-resultant signal according to a temporary decision algorithm, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; fifth means for calculating a difference between the temporary decision value of the equalization-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; sixth means for controlling the tap coefficients of the transversal filter in response to the error signal generated by the fifth means so as to minimize the error signal; and seventh means for setting the temporary decision algorithm used by the temporary decision device to a first predetermined algorithm corresponding to PR (a, b, b, a) when the fourth means selects the 0-point information, and setting the temporary decision algorithm used by the temporary decision device to a second predetermined algorithm corresponding to PR (a, b, xe2x88x92b, xe2x88x92a) when the fourth means selects the peak-point information.
A twelfth aspect of this invention is based on the eleventh aspect thereof, and provides a reproducing apparatus wherein the second means and the third means comprise an A/D converter for converting the signal reproduced by the first means into a digital signal, means for subjecting the digital signal generated by the A/D converter to a re-sampling process to generate a re-sampling resultant signal, means for feeding the re-sampling resultant signal to the transversal filter, means for detecting whether or not the digital signal generated by the A/D converter corresponds to a zero-cross point, and generating 0-point information in response to a result of said detecting, and means for detecting whether or not the digital signal generated by the A/D converter corresponds to a peak point, and generating peak-point information in response to a result of said detecting.
A thirteenth aspect of this invention provides a reproducing apparatus comprising first means for reproducing a signal of a run-length-limited code from a recording medium; a transversal filter subjecting the signal reproduced by the first means to a partial-signal, response waveform equalization to generate an equalization-resultant the partial-response waveform equalization depending on tap coefficients; second means for detecting whether or not the equalization-resultant signal generated by the transversal filter corresponds to a zero-cross point, and generating 0-point information in response to a result of said detecting; third means for detecting whether or not the equalization-resultant signal generated by the transversal filter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; fourth means for selecting one of the 0-point information generated by the second means and the peak-point information generated by the third means; a delay circuit responsive to the point information selected by the fourth means for outputting at least three successive samples of the selected point information; a temporary decision device for calculating a temporary decision value of the equalization-resultant signal on the basis of a PR mode signal, an RLL mode signal, the successive samples of the selected point information which are outputted from the delay circuit, and an actual value of the equalization-resultant signal according to a temporary decision algorithm, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; fifth means for calculating a difference between the temporary decision value of the equalization-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; sixth means for controlling the tap coefficients of the transversal filter in response to the error signal generated by the fifth means so as to minimize the error signal; and seventh means for setting the temporary decision algorithm used by the temporary decision device to a first predetermined algorithm corresponding to PR (a, b, b, a) when the fourth means selects the 0-point information, and setting the temporary decision algorithm used by the temporary decision device to a second predetermined algorithm corresponding to PR (a, b, xe2x88x92b, xe2x88x92a) when the fourth means selects the peak-point information.
A fourteenth aspect of this invention is based on the tenth aspect thereof, and provides a reproducing apparatus further comprising a viterbi decoder for subjecting the equalization-resultant signal to a decoding process, and fifth means for changing the decoding process in response to whether the temporary decision algorithm is set to the first predetermined algorithm or the second predetermined algorithm.
A fifteenth aspect of this invention is based on the tenth aspect thereof, and provides a reproducing apparatus wherein the signal reproduced from the recording medium by the first means comprises a first signal and a second signal, and the temporary decision algorithm is set to the first predetermined algorithm for the first signal and is set to the second predetermined algorithm for the second signal.
A sixteenth aspect of this invention is based on the tenth aspect thereof, and provides a reproducing apparatus wherein the first means comprises means for reproducing the signal of the run-length-limited code from the recording medium in a tangential push-pull method.